Implantable Cardiac Defibrillator (cont.)
What is the cause of tachycardias?
Abnormally fast heart rates are called tachycardias.
Tachycardias are caused by rapidly firing electrical
signals arising from the walls of the atria or the
ventricles. These rapidly firing signals override the
signals generated by the SA node and cause the heart to
beat too fast.
Tachycardias caused by electrical signals from the atria
are called atrial tachycardias. Tachycardias caused by
electrical signals from the ventricles are called ventricular tachycardias.
What are the symptoms of tachycardias?
Symptoms of tachycardias include:
- Palpitations or fluttering sensations in the heart;
- Lightheadedness (due to low blood pressure);
- Fainting spells or loss of consciousness (due to low blood pressure);
- Fatigue and weakness (due to lack of blood supply); and
- A flushing sensation.
Please see the Palpitations article
of MedicineNet.com for information on the symptoms, causes, and diagnosis of
tachycardias.
What are life-threatening tachycardias?
Two common life-threatening tachycardias are ventricular
tachycardia and ventricular fibrillation. Ventricular
tachycardia is a rapid regular rhythm caused by electrical
signals originating from an area of the ventricle.
Ventricular tachycardia can decrease blood delivery by the
heart and cause low blood pressure. Ventricular tachycardia
can also progress to a more serious heart rhythm called
ventricular fibrillation.
Ventricular fibrillation is an irregular rhythm, which
is a result of multiple rapid and chaotic electrical
signals firing from many different areas in the ventricles.
A heart undergoing ventricular fibrillation is in a state
of standstill called cardiac arrest. The heart muscles
quiver and cease pumping which causes a halt in the
delivery of blood to the body. Unless ventricular
fibrillation is terminated quickly, irreversible brain
damage occurs within minutes of the onset of ventricular
fibrillation, leading to death.
Sudden cardiac arrest is the most common cause of death
in the United States. About 450,000 Americans suffer
cardiac arrest each year. 80 to 90% of these patients die
before reaching the hospital. The most frequent causes of
cardiac arrest in the United States are ventricular
tachycardia and ventricular fibrillation.
Next: What are the causes of ventricular tachycardia and ventricular fibrillation? »
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